TY  - JOUR
AU  - Banerjee, P.
AU  - Coutinho, A.
AU  - Engel, T.
AU  - Gurgone, A.
AU  - Signer, A.
AU  - Ulrich, Y.
PY  - 2023
DA  - 2023//
TI  - High-precision muon decay predictions for ALP searches
T2  - SciPost Phys.
JO  - Scipost Physics
SP  - 021
EP  - 38pp
VL  - 15
IS  - 1
PB  - Scipost Foundation
AB  - We present an improved theoretical prediction of the positron energy spectrum for the polarised Michel decay & mu;+ & RARR; e+ & nu;e & nu; over bar & mu;. In addition to the full next-to-next-to-leading order correction of order & alpha;2 in the electromagnetic coupling, we include logarithmically enhanced terms at even higher orders. Logarithms due to collinear emission are included at next-to-leading accuracy up to order & alpha;4. At the endpoint of the Michel spectrum, soft photon emission results in large logarithms that are resummed up to next-to-next-to leading logarithmic accuracy. We apply our results in the context of the MEG II and Mu3e experiments to estimate the impact of the theory error on the branching ratio sensitivity for the lepton-flavour-violating decay & mu;+ & RARR; e+X of a muon into an axion-like particle X.
SN  - 2542-4653
UR  - https://arxiv.org/abs/2211.01040
UR  - https://doi.org/10.21468/SciPostPhys.15.1.021
DO  - 10.21468/SciPostPhys.15.1.021
LA  - English
N1  - WOS:001038392400002
ID  - Banerjee_etal2023
ER  -